Cameron Diaz wishes she had given Fiona in 'Shrek' a British accent.

The US actress - who has voiced ogress Fiona in all four of the movies - would have rid herself of her Californian accent had she known the green-skinned character's parents were being voiced by Julie Andrews and John Cleese in the second film.

She said: "If I had known that Fiona's parents both had British accents when I first started - that they were being voiced by Julie Andrews and John Cleese, I might have, you know.because when I first started the movie, when I did my voice, I didn't know who was playing my parents.

"So it was one of those things where I was like, 'Wait a second! How come I sound like I am from California?' "

The 37-year-old beauty also claims the film is suitable for both adults and children as it teaches everyone the lessons of love and life.

She told About.com: "You're never too old or too young to learn these lessons, and I think that's the case with all the 'Shrek' films and why they're so successful. They're not just speaking to one audience, they're speaking to everyone. Anyone who watches it can understand exactly what Shrek and Fiona are going through relevant to their own lives."

'Shrek Forever After' - the final movie in the franchise - is due for release on May 21.